Monoclonal antibodies were screened for the ability to block the motility of human A2058 melanoma cells. A monoclonal antibody was identified which arrested tumor cell motility without altering adhesion. The antigen recognized by the antibody is a glycosylated cell surface protein with a molecular weight of 95 kDa. This antibody was used to screen a cDNA library. The cDNA clone isolated encodes a unique protein. Homology is noted with CD4, N-CAM and certain ion channel proteins. The predicted sequence has a transmembrane domain. Future plans include a structure-function analysis of this protein as a regulatory of motility and a correlative analysis of the levels of the protein or its mRNA associated with various stages of tumor progression.